The Endoplasmic Reticulum (ER) is an important and geometrically complex organelle within most living cells that can form highly dynamic network-like structures within the cell. This talk will discuss a study of some of these dynamic network structures within plant cells based on live cell imaging of movies showing dynamic ER networks. We hypothesise that the structures observed are minimal geometric networks perturbed by deterministic (cytoplasmic streaming) and random (Brownian) forces. We also try to quantify the biophysics behind the structures (joint work with Imogen Sparkes, Congping Lin and Yiwei Zhang).